Individual engine cylinders may undergo a misfire event wherein a combustion event does not occur as intended. For engines with multiple cylinder banks, there may be conditions where every cylinder in a given bank misfires, resulting in a cylinder bank misfire. Engine control systems may include misfire detection modules for identifying such misfire events. As an example, engine misfire can be identified based on fluctuations in the crankshaft torsional vibration as detected by a crankshaft acceleration sensor.
However, the inventors herein have recognized potential issues with such detection methods that rely on a crankshaft acceleration sensor. By detecting misfire solely based on crankshaft acceleration sensor response, erroneous detection may take place. For example, in vehicles equipped with dual or variable mass flywheels (DMF) or pendulum dampers for reducing torsional vibrations in the vehicle, engine operations at certain speed levels may excite a resonant frequency in the DMF. This can result in crankshaft torsional vibrations that may be erroneously detected by the crankshaft acceleration sensor as a misfire event. As such, if an engine cylinder is deactivated in response to an indication of misfire, overall engine performance may be affected. Also, on-board diagnostic routines may be impacted by such inaccurate misfire indications.
The inventors herein have identified an approach by which the issues described above may be at least partly addressed. One example method for a boosted engine comprises: during dual mass flywheel (DMF) operation within a threshold range of a resonant frequency, indicating cylinder misfire based on each of a crankshaft torsional vibration, an exhaust air fuel ratio, and an exhaust gas temperature. In this way, by relying on a plurality of detection techniques selected based on operating conditions, cylinder misfire detection may be carried out more reliably even in the presence of DMF resonance.
As one example, an engine may be coupled to an automatic transmission via a dual mass flywheel, such as a pendulum damper. An engine misfire detection module of the engine may receive input from each of a crankshaft acceleration sensor, an exhaust gas oxygen sensor, and an exhaust gas temperature sensor. Upon detection of higher than threshold level of fluctuations in crankshaft torsional vibration based on a crankshaft acceleration sensor response, the controller may determine if the DMF is operating within a threshold resonant frequency range at the current vehicle speed. If it is determined that the DMF is operating within a threshold resonant frequency range, instead of indicating misfire in one or more cylinders based on only the crankshaft accelerator response, the misfire detection module may assess one or more additional parameters indicative of a misfire event to increase a confidence value of the misfire detection. For example, the controller may additionally monitor an air fuel ratio estimated by the exhaust gas oxygen sensor. If the air fuel ratio is higher than a threshold air-fuel ratio, optionally an exhaust gas temperature may also be monitored via the exhaust gas temperature sensor. If it is determined that the exhaust gas temperature is lower than a threshold temperature (while the air fuel ratio is higher than the threshold air-fuel ratio and fluctuations in crankshaft torsional vibration are higher than the threshold level), misfire detection may be confirmed, and one or more misfiring cylinders may be suitably deactivated. In still other examples, based on the presence of DMF vibration, the thresholds for each of the parameters may be updated. The deactivated cylinders may be selectively reactivated once it is confirmed that the DMF is no longer operating within the threshold resonant frequency range. If the DMF continues to operate within the threshold resonant frequency range even after a threshold period of time following cylinder deactivation, one or more engine actuators may be shifted to change engine speed such that the DMF operating frequency correspondingly changes. For example, a transmission gear may be downshifted, a torque converter slip schedule may be varied to decouple vibration input into transmission, etc. If upon cylinder reactivation, a misfire is detected again in an individual cylinder, then that cylinder may be selectively deactivated for a remainder of the engine operation with remaining cylinders in the bank being operated in an active state. Also, a flag may be set indicating the identity of the misfiring cylinder.
In this way, by relying on the output of a plurality of sensors including a crankshaft acceleration sensor, an exhaust gas oxygen sensor, and an exhaust gas temperature sensor for misfire detection, engine vibration due to misfire may be better distinguished from vibration resulting from DMF operation. The technical effect of relying on multiple parameters indicative of misfire during conditions of increased DMF vibration is that misfire detection accuracy is increased and engine cylinders may be held active for a longer duration. By reactivating cylinders upon confirmation of DMF operation out of a resonant frequency range, further erroneous misfire detection for the reactivated cylinders may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.